This invention relates in general to pumps and in particular to a new and useful proportioning pump for liquids which includes a pump piston which is movable in an uptake valve cylinder which itself is movable and driven by a separate drive.
The invention concerns a proportioning pump for liquids including a piston in a cylinder, an uptake and discharge valve and oscillating drive. A similar piston proportioning pump is described in German OS No. 33 31 558. It is used to proportion smallest amounts of liquid or gaseous media accurately and reproducibly. It consists of a piston moving in a cylinder which exerts periodical suction and compression strokes driven by an oscillating drive, e.g. a crank mechanism. An uptake as well as a discharge valve open into the pump space.
The known proportioning pumps have the disadvantage that a drop in pressure occurs during the suction phase with opened uptake valve due to the resistance of the usually narow uptake valve, which results in the formation of vapor bubbles during the lifting of liquids with a high vapor pressure, or in incomplete filling in the pump space during the lifting of gaseous media. An exact proportioning is thereby made impossible. An expulsion of the formed vapor bubbles during the subsequent compression stroke, when the liquid is pressed out of the pump space through the discharge valve, is not guaranteed. The exact and reproducible proportioning of smallest amounts of liquid or gaseous media in the miroliter range requires the lowest possible flexibility of the pressure chamber and its contents including--no bubbles in the liquid which raise the compressibility dramatically--rigid pressure chamber walls--minimal flexibility of the valves themselves minimal dead space; so that the proportioned volume to be expelled can be moved in its entirety into the discharge line. Beyond this, more stringent demands must be made on the uptake as well as the discharge valve with respect to the prevention of leakages. With the known piston proportioning pump, the opening of the uptake valve during the occurrence of excess pressure in the feeding line and the escape of the medium to be proportioned throug the pump space and the discharge valve directly into the feeding line cannot be prevented. A proportioning is no longer possible in this case and an uncontrolled flow of medium to the user side occurs.